Encoder, decoder, encoding method, and decoding method

Provided is an encoder including: circuitry; and memory coupled to the circuitry, in which the circuitry: derives a prediction residual indicating a difference between a current block and a prediction image of the current block; performs primary transform on the prediction residual, and performs secondary transform on a result of the primary transform; performs quantization on a result of the secondary transform; and encodes a result of the quantization. In the performing of the secondary transform, when a matrix weighted intra prediction included in intra prediction and having prediction modes is used, the circuitry uses, as a transform set for the secondary transform, a common transform set shared among the prediction modes. The matrix weighted intra prediction generates the prediction image by performing matrix calculation on a pixel sequence obtained from pixel values of surrounding pixels of the current block.